1. Field of the Invention
The present invention is directed to an electromagnetic relay, and more particularly, to such a relay in which an armature and a yoke are magnetically coupled partially within an elongated coil bobbin carrying an excitation coil.
2. Description of the Prior Art
In recent years there has been a growing demand for relays, particularly for power relays which switch a relatively high current but can be made compact enough to be fitted within a limited space. U.S. Pat. Nos. 4,689,587 and 4,720,694 proposed a relay in which an armature and a yoke have their portions inserted respectively within a coil bobbin carrying an excitation coil and are magnetically coupled together within the coil bobbin in order to obtain a compact design for arrangement of the coil bobbin, the armature, and the yoke within a limited space. The armature is pivotally supported on the yoke at a position outwardly of the coil bobbin to be pivotable about a pivot axis between a set position of closing a relay contact and a reset position of opening the relay contact. In order to retain the armature in a proper position for effecting the pivotal movement, a leaf spring is utilized to tie the armature and the yoke together. In this patent, however, since the armature has its pivot axis outside of the coil, the leaf spring is required to be placed exteriorly of the coil bobbin to tie the armature and the yoke at positions outwardly of the coil bobbin. Such spring arrangement adds to the dimensions of the relay assembly and should be avoided for providing a relay as compact as possible. Further, since the leaf spring utilized in the patent is elongated to extend substantially the full length of the yoke and be secured to the armature and the yoke at opposite ends, the leaf spring may have more chances to be deformed in the lengthwise direction at the assembly of the relay as well as at the forming of the spring, which might lead to an unacceptable variations in spring characteristic and fail to give a constant spring bias required to retain the armature at an exact position relative to the yoke for the pivotal movement thereof. For instance, when the spring gives only a weak biasing force the armature will see undesirable shifting of the pivot axis during the pivot movement, and when the spring gives a strong biasing force the armature will be reluctant to move in response to the energization of the coil and therefore have lowered response sensitivity, both of which would result in unstable relay operations and therefore be the causes of increased fraction defective. Consequently, the prior art relay is still found unsatisfactory from the standpoint of providing a more compact design with reliable operational characteristics.